1. Field of the Invention
The invention relates to a method for manufacturing a polarizing plate by bonding a first and a second transparent protective films to both sides of a polarizer with an adhesive layer interposed therebetween.
2. Description of the Related Art
In a process of manufacturing a polarizing plate in related art, a water-based adhesive or pressure-sensitive adhesive is generally used to bond transparent protective films to both sides of a polarizer having a predetermined water content. Examples of the method used to bond transparent protective films to both sides of a polarizer include a simultaneous lamination method that includes feeding a polarizer between a pair of rolls and feeding transparent protective films to both sides of the polarizer so that the transparent protective films can be simultaneously bonded to both sides; and a sequential lamination method that includes feeding a polarizer between a pair of rolls, feeding a transparent protective film to one side of the polarizer to bond it to the one side, and then bonding another transparent protective film to the other side of the polarizer.
Unfortunately, these lamination methods have a problem in that bubbles can be formed between the polarizer and the transparent protective film in the process of obtaining the polarizing plate by bonding the transparent protective films to the polarizer.
To solve this problem, JP-A-2008-037092 proposes a sequential lamination method that includes allowing a polarizer and a first transparent protective film to pass between a pair of a first metal roll and a first elastic roll in such a manner that the first transparent protective film is placed on the first metal roll side, so that they are pressure-bonded to form a laminated film; and then allowing the laminated film without winding it and a second transparent protective film to pass between a pair of a second metal roll and a second elastic roll in such a manner that the second transparent protective film is placed on the second metal roll side, so that they are pressure-bonded to form a polarizing plate.
JP-A-2010-125702 proposes a method for manufacturing a laminated film, which includes purging entrained air from film surfaces with replacement gas having a water solubility of 0.1 cm3/cm3H2O (20° C., 1 atm) or more and bonding films together while the air on the surface of each film is replaced with the replacement gas.
In addition, JP-A-2002-365432 proposes that a polarizing film and a protective film should be bonded together with an adhesive whose viscosity is adjusted to 3 to 20 mPa·s (25° C.) JP-A-2008-122790 describes a method for manufacturing a polarizing plate by bonding transparent protective films with different thicknesses to both sides of a polarizer. The techniques disclosed in JP-A-2002-365432 and JP-A-2008-122790 are applicable to the simultaneous lamination method. However, JP-A-2002-365432, which aims to improve the appearance of a polarizing plate, or JP-A-2008-122790, which aims to suppress curling of a polarizing plate, does not necessarily remedy the problem of bubbles mentioned above.